The present invention relates to a cassette tape-loading apparatus suitable for a magnetic recording and reproducing system using a cassette tape.
A magnetic recording and reproducing system for recording and reproducing a signal by the use of a cassette tape uses a mechanism for drawing a magnetic tape out of a tape cassette and loading it on a predetermined tape running path around a rotative cylinder.
In conventional cassette tape-loading apparatuses, in order to prevent the magnetic tape from falling off a predetermined tape running path at the time of loading, a predetermined torque is applied to reel motors for rotating a supply reel and a take-up reel and giving a tension to the magnetic tape in the loading process.
Also, in a tape-loading apparatus disclosed in JP-A-63-9055, the rotational speed of each reel motor is detected at the time of loading a tape, and the torques applied to the reel motors are regulated in accordance with variations in rotational speed.
Specifically, the rotational speed of the reel motor for driving a reel on which the tape is wound is compared with a reference speed, so that
(1) when the rotational speed of the reel motor is higher than the reference speed, torque setting means is used to apply a torque corresponding to a predetermined tension to the reel motor in accordance with the loading or unloading mode, whereas
(2) when the rotational speed of the reel motor is lower than the reference speed, the torque is applied by a speed loop circuit to attain the reference speed.
In this way, the damage to the tape due to the tape guide and the like is alleviated on the one hand while improving the tape-positioning accuracy on the other hand in the tape loading and unloading operations.
In the above-described conventional tape-loading apparatuses, however, no consideration is given to the amount of winding of the magnetic tape on the supply and take-up reels, that is, the winding diameter (radius) of the supply and take-up reels, thereby posing many problems including the tape being damaged due to an abnormal tension applied thereto or coming off from a predetermined tape running path at the time of loading.
At the time of loading a tape in the prior art, the reel motors for driving the supply and take-up reels are supplied with the same torque. In the case where the supply and take-up reels have different winding diameters, therefore, the magnetic tape on a reel of smaller winding diameter is subjected to a tension larger than a predetermined level, while a tension smaller than the predetermined one is applied to the magnetic tape running on the reel of larger winding diameter. As a result, an excessive tension is liable to damage the tape, cause the tape to loosen and come off the predetermined running path or cause the tape to be damaged by the edge of the tape guide. The imbalance in tension between supply and take-up reels, on the other hand, causes the magnetic tape to run in one direction, so that the repetition of the loading and unloading operations of the magnetic tape may lead to the problem of the recording or reproducing position greatly displaced on the magnetic tape. Even when the rotational speeds of the reels are detected and the torques to the reel motors regulated as described with reference to JP-A-63-9055 above, the linear speed of the magnetic tape drawn out of the supply or take-up reel is incapable of being controlled while the tape is being loaded, if the winding diameter is not known, and therefore it is impossible to prevent the unidirectional running of the magnetic tape. Nor is it possible to prevent an abnormal tension to apply a proper tension to the magnetic tape in the tape-loading operation.
A VTR for commercial use, such as a digital VTR of D-2 format ("Proposed American National Standards", SMPTE 244M, 255M, 246M, 247M, 248M) has three tape cassette sizes of "L", "M" and "S". Further, the "M"-sized tape cassette ranges from a minimum recording time of a few minutes to a maximum recording time of 94 minutes covering a wide range of reel-winding diameters. If the torque of a reel motor is set for the tape-loading operation without taking the winding diameter into consideration, therefore, the tape would be damaged very often.